Epitaxial growth of ultrathin layers on the surface of sub-10 nm nanoparticles: the case of β-NaGdF 4 :Yb/Er@NaDyF 4 nanoparticles.

Upconversion core-shell nanoparticles have attracted a large amount of attention due to their multifunctionality and specific applications. In this work, based on a NaGdF 4 sub-10 nm ultrasmall nanocore, a series of core-shell upconversion nanoparticles with uniform size doped with Yb 3+ , Er 3+ and NaDyF 4 shells with different thicknesses were synthesized by a facile sequential growth process. NaDyF 4 coated upconversion luminescent nanoparticles showed an obvious fluorescence quenching under excitation at 980 nm as a result of energy resonance transfer between Yb 3+ , Er 3+ and Dy 3+ . NaGdF 4 :Yb,Er@NaDyF 4 core-shell nanoparticles with ultrathin layer shells exhibited a better T 1 -weighted MR contrast.